Mr Johnson yesterday saw his plan to target senior Russian and Syrian military figures dismissed by European nations at a G7 meeting in Italy.

The outcome had been branded an embarrassment for the Foreign Secretary, who had publicly voiced his wish for punishment for the two regimes in the wake of the horror chemical weapons attack on Syrian civilians.

The sarin gas attack, which included a number of children among the victims, has been blamed on Syria’s brutal dictator Bashar al-Assad – whose government is supported by Russian president Vladimir Putin.

Although foreign ministers agreed to brand the gas attack a war crime and pledged a United Nations investigation, Italy and France are believed to have led opposition to Mr Johnson’s proposals for new sanctions.

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Mr Hammond, who was Mr Johnson’s predecessor at the Foreign Office but has recently endured a spiky relationship with his Cabinet colleague, insisted Britain was right to demand a “robust” approach to Russia’s involvement in Syria.

The Chancellor told Sky News: “The British Government's position has been, and will remain, to lead the way on arguing for a robust approach towards Russian aggression in Syria.

"We have been doing it for years and we will go on doing it. We have to make that case and we will continue making that case.

"Sometimes some of our partners are less forward-leaning than we are but that won't stop us making the case for what we believe is the right approach to dealing with Russia."

Sometimes some of our partners are less forward-leaning than we are but that won't stop us making the case

Philip Hammond

Mr Johnson also found support from fellow Tory MP Alistair Burt who claimed he was “disappointed” there was a focus on the Foreign Secretary’s performance at the G7 summit rather than “a way to end this conflict in which one out of two Syrians have either died or been displaced”.

But Labour’s shadow chancellor John McDonnell claimed Mr Johnson's failure to get other G7 nations to back his push for new sanctions had damaged Britain’s credibility in the world.

He said: “The idea of going along to the G7 and threatening to try and put together a coalition around sanctions was never going to succeed.

“It was a really bad policy decision by Mr Johnson. It should never have happened. It is a pity that Mr Johnson made such a poor judgment in this matter.

"To have these one day on and off policies from Boris Johnson every time he thinks up a new idea, never really thinks it through, and then embarrasses our whole country in the international scene, to be frank, undermines our credibility in the future.”

At least 58 people, including nine children, were killed in an air raid that released "toxic gas" on the rebel-held Syrian town of Khan Sheikhoun

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A child receiving treatment at a field hospital after an alleged chemical attack in Idlib, northen Syria

Mr McDonnell, who saw his party leader Jeremy Corbyn refuse to answer questions on the Syria crisis at one point yesterday, also called on Theresa May to end her current walking holiday in Wales to deal with the situation.

He added: "I don't begrudge anyone a break every now and again.

“But, you have got to either recognise the seriousness of the situation and put your full attention to it, and that is what I think the Prime Minister should be doing, or you have got to have confidence in the person that you send out to deal with this situation.

"What we've got at the moment is neither a Prime Minister properly engaged, nor someone who anybody, even on Tory backbenches, and in, what we understand, the Government's own Cabinet, has confidence in with regard to Boris Johnson.

“I think we are in the worst of all worlds as a result."

After yesterday’s summit ended, a spokesman for Mr Johnson said: “The Foreign Secretary was the one this week at the G7 calling for tough action against those who have killed innocent people.

“Some may criticise but it was simply the right thing to do to try to push other countries to punish war criminals and murderers.

“Frankly, it is completely shortsighted and wrong to claim this G7 failed to deliver. It unanimously agreed Assad has no future in Syria, that Russia must work to stabilise Syria and work with others, and everyone round the table agreed that sanctions should and would be imposed on those involved in the chemical weapons attack once an investigation happens.”